Most golf balls fall into one of several general types of ball construction. Two piece balls comprise a solid core and a cover. Three piece or wound balls traditionally comprise a solid or liquid filled center wound with an elastic thread and covered with another material, usually trans polyisoprene or an ionomer. Recently, the term "three piece" has also been used in reference to golf balls having a center inside of a solid mantle of a polybutadiene having a compression different than the compression of the center.
Golf balls having a liquid filled center have been known for many years. Liquid centers are used extensively in three piece balls. Liquid centers have been traditionally made by incorporating a small amount of water between two sheets of natural rubber and then making round punches having sealed edges from the two sheets of rubber. Afterward, these circular punches are put in spherical mold cavities, and heated, whereupon the water in the punch expands forcing the rubber material against the hot walls of the mold. Hollow spheres so produced are filled with a solution of liquid by piercing the hollow rubber sphere with a needle syringe and then injecting the liquid into the center. The needle syringe, however, produces a puncture hole in the ball which must be sealed to prevent leakage of the liquid filling material.
In the past this puncture hole has been sealed with a two-component polyurethane adhesive. Although two-component urethanes have proven effective for sealing the puncture hole, these urethanes tend to generate undesirable volatile organic compounds ("VOC"). Also, such two-component urethanes tend to crack when applied to flexible surfaces. Two-component urethanes, moreover, tend to be slow curing, typically requiring more than about one hour to cure at room temperature.
There is therefore a need in the golf ball art for a solution to the problem of sealing the injection hole in liquid filled golf ball centers which overcomes the disadvantages of the prior art.